When energy relaxation between electrons and the lattice is slow, an elevated electronic temperature different from that of the lattice persists. In this regime, hot charge carriers control the energy transport in a material. In this thesis, I show how hot carriers can dominate graphene's response enabling it to exhibit novel properties. First, I examine how light is converted to electrical currents in graphene and show that hot carriers play an integral role in this multi-stage process. I show that photocurrent in graphene p-n junctions is dominated by a Photo-thermoelectric effect in which a light-induced elevated hot carrier temperature drives a thermoelectric current. Furthermore, I show that the generation and cooling of hot carriers in graphene during photoexcitation proceeds in an unusual way. In the former, carrier-carrier scattering dominates the initial photoexcitation cascade enabling efficient hot carrier generation. In the latter, a new cooling mechanism - disorder-assisted scattering (supercollisions) - dominates electron-lattice cooling over a wide range of temperatures (including room temperature). Second, I examine the transport characteristics of double layer graphene heterostructures (specifically, G/h-BN/G heterostructures). I show that Coulomb coupling results in vertical (out-of-plane) energy transfer between electrons in proximal (but electrically insulated) graphene layers. This couples lateral (in-plane) charge and energy transport of electrons in the two layers to give rise to a new energy-driven Coulomb drag (inter-layer transresistance) that dominates when the two layers are at charge neutrality. Third, I examine energy transport in charge neutral graphene. I show that the combination of fast carrier-carrier scattering, high electronic quality, and slow electron-lattice cooling (hot carriers) gives rise to a regime of ballistic heat transport. This manifest as electronic energy waves with velocity on the order of graphene's Fermi velocity. The new phenomena enabled by hot carriers and the ideas/approaches described in this thesis provide a basis with which to exploit hot carrier effects in graphene and opens new vistas for controlling and harnessing energy flows on the nanoscale. / Engineering and Applied Sciences

Not available / text

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The use of solid dispersions to formulate poorly water soluble drugs is a growing field in the pharmaceutical sciences. Hot-melt extrusion is a common method for producing dispersions. However, bench-top extruders require large amounts of powder to run and are inappropriate for early formulation screens. Plastic and glass syringes are readily available in most laboratories. 250 mg of drug-polymer blend is placed in a plastic syringe body that has the tip covered with a bent needle. The syringe is heated for 5 minutes and the extrudate is pushed through the syringe. Extrudates are characterized by differential scanning calorimetry and powder x-ray diffraction. Acetaminophen, griseofulvin, indomethacin, salicylamide, and sulfamethoxazole extruded with polyvinylpyrrolidone K12 match or exceed the performance of solvent evaporated controls. Glass syringes can be used when polymers have processing ranges above the melting point of the plastic syringes. Syringe extrusion is effectively demonstrated as a rapid process for early formulation screening.

This dissertation explores the atmospheric circulation of extrasolar planets ranging from hot Jupiters to super Earths. For each of these studies, I utilize a three-dimensional circulation model coupled to a state-of-the-art, plane-parallel, two-stream, non-grey radiative transfer model dubbed the SPARC/MITgcm. First, I present models of the atmospheric circulation of eccentric hot Jupiters, a population which undergoes large variations in flux throughout their orbits. I demonstrate that the eccentric hot Jupiter regime is qualitatively similar to that of planets on circular orbits. For a select number of model integrations, I generate full-orbit lightcurves and find that the timing of transit and secondary eclipse viewed from Earth with respect to periapse and apoapse can greatly affect what is seen in infrared (IR) lightcurves. Next, I present circulation models of WASP-43b, a transiting hot Jupiter that is joining the ranks of HD 189733b and HD 209458b as a 'benchmark' hot Jupiter, with a wide array of observational constraints from the ground and space. Here I utilize the robust dataset of spectrophotometric observations taken with the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) to interpret my model results. I find that an atmospheric composition of 5x solar provides the best match to the data, particularly in emission. Lastly, I present atmospheric simulations of the super Earth GJ 1214b, exploring the planet's circulation as a function of atmospheric metallicity and composition. I find that atmospheres with a low mean-molecular weight have strong day-night temperature variations at pressures above the infrared photosphere that lead to equatorial superrotation. For these atmospheres, the enhancement of atmospheric opacities with increasing metallicity leads to shallower atmospheric heating, larger day-night temperature variations and hence stronger superrotation. In comparison, atmospheres with a high mean-molecular weight have larger day-night and equator-to-pole temperature variations than low mean-molecular weight atmospheres, but differences in opacity structure and energy budget lead to differences in jet structure. By comparing emergent flux spectra and lightcurves for 50x solar and water-dominated compositions, I show that observations in emission can break the degeneracy in determining the atmospheric composition of GJ 1214b. In sum, these three studies explore exoplanet atmospheric circulation as a function of mass, radius, gravity, rotation rate, eccentricity and orbital distance.

The main objectives of this research are (a) to investigate the thermal effect of double skin facades in office buildings in hot climates and (b) to propose guidelines for their efficient design based on this evaluation. The study involves the energy performance analysis of two buildings in India. A base case with the existing building skin was simulated for both the cities. The main source for the high cooling loads was found to be heat gain through windows and walls. This led to the evolution of a series of facade strategies with the goals of reducing heat gain, providing ventilation and day-lighting. The buildings were then simulated for their energy performance with the proposed double-skin strategies. Each of these strategies was varied according to the layers constituting the facade, the transparency of the facade and the orientation of the facade to which it is applied. Final comparisons of energy consumption were made between the proposed options and the base case to find the most efficient strategy and also the factors that affected this efficiency. The simulations were done using the building simulation software, Ener-Win. The double skin was simulated as per an approximate and simplistic calculation of the u-value, solar heat gain coefficient and transmissivity properties of the layers constituting the facade. The model relied on logically arrived at assumptions about the facade properties that were approximately within 10% range of measured values. Based on inferences drawn from these simulations, a set of design guidelines comprised of goals and parameters was generated for design of double-skin facades in hot climates typical to most of the Indian subcontinent. It was realized that the double-skin defined typically as a 'pair of glass skins separated by an air corridor' may not be an entirely energy efficient design strategy for hot climates. However, when used appropriately in combination with other materials, in the right orientation and with the right transparency, a double-layered facade turns out to be an energy efficient solution.

Vor allem in der Schmerzforschung spielt eine Erfassung der Schmerztoleranzschwellen eine große Rolle. Ziel unserer Studie war es, die ideale Stimulationstemperatur zur Messung der Schmerztoleranz zu erarbeiten. In älteren Studien wurden diese Methoden bereits untersucht, entsprachen aber nicht den Kriterien evidenzbasierter Forschung. Zu diesem Zweck wurde eine randomisierte, kontrollierte Studie an 100 Probanden durchgeführt. Eine Verblindung fand nicht statt. Zum Einsatz kamen fünf Tests, zum einen der „cold-pressor“-Test, der Elektrostimulationstest, sowie drei „hot-pressor“-Tests bei 45°C, 47°C und 49°C. Die Studie fand bei standardisierten Testbedingungen im Rahmen von insgesamt fünf Sitzungen statt, in denen je einer der oben genannten Tests durchgeführt wurde. Potentielle Beeinflussung der nicht-gewünschten Umgebungsfaktoren auf die Studienergebnisse wurde durch standardisierte Testbedingungen so weit wie möglich minimiert. Insgesamt gab es bei keinem der Probanden unter den oben genannten maximalen Schmerzstimulationsexpositionen lang anhaltende unerwünschte Nebenwirkungen oder sensorische Störungen. Im Vergleich zu früheren Studien konnten bei einer deutlich höheren Probandenzahl die Kälteschmerztoleranzschwellenwerte bestätigt werden. Zu erkennen ist, dass die Variabilität der Inter-Probanden-Schwellenwerte bei elektrischen Reizen am niedrigsten ist, wahrscheinlich aber bedingt durch die Tatsache, dass viele Probanden maximal erlaubte Stromstärke tolerierten. Eine Heißwasserbadtemperatur von 45°C wird auch bei mehr als 60% der Probanden bis zu unserer gemessenen Maximaldauer von 300 Sekunden toleriert und bei einer Temperatur von 47°C von fast 10% der Probanden problemlos toleriert. Eine Wärmestimulation („hot-pressor“-Test) des Unterarmes im Heißwasserbad mit 49°C wird bei nur einem von 100 Probanden in der maximal erlaubten Zeit der Stimulation toleriert. Die Inter-Probanden-Variabilität ist vergleichbar zur Kaltwassertoleranz, jedoch ohne Korrelation der beiden Tests zueinander. Die gefundene hohe Variabilität der NRS-Werte bei allen Schmerzstimulationen hebt die Notwendigkeit einer detaillierten Definition der „tolerierten Schmerzintensität“ bei diesen Studien hervor.

Abstract   Hot mot journalister är inget nytt fenomen. Däremot är debatten kring denna problematik mer aktuell än någonsin. Samtidigt råder det en viss brist på vetenskapliga undersökningar, som går på djupet vad gäller enskilda journalister och deras erfarenheter av hot. Det huvudsakliga syftet med denna uppsats är därför att utforska åtta journalisters upplevelser i samband med sådana. Utöver detta kommer jag dessutom att analysera hotupplevelserna utifrån journalistikens uppgifter enligt olika demokratimodeller.  Mina teoretiska verktyg består vid sidan av teorier rörande olika demokratimodeller och deras syn på journalistik av känslo- och problemfokuserade copingstrategier mot vilka jag kommenterar journalisternas upplevelser. Vad gäller metod har jag intervjuat respondenterna i enlighet med en semistrukturerad intervjuform samt använt mig av en kvalitativ innehållsanalys. När det kommer till frågan om hur mina respondenter påverkas av hot på ett mentalt plan är några av fallen särskilt anmärkningsvärda. En av journalisterna talar i termer av en slags depression medan en annan berättar att han, som en konsekvens av de hot han utsatts för, ibland överreagerar i helt oskyldiga situationer. Samtidigt har ingen av de journalister, som ingår i denna undersökning, någonsin övervägt att ge upp sitt yrke och det är dessutom relativt ovanligt att man avstår eller modifierar en text på grund av rädsla för repressalier. Mina resultat visar dock att hot mot journalister samt eventuella konsekvenser kan ha en negativ effekt på olika demokratiska ideal. Frågan huruvida dessa hot utgör ett demokratiskt problem är på samma gång en komplex fråga, som är beroende dels av vilka journalistiska uppgifter anammad demokratimodell kräver och dels på situation. Till sist har arbetsgivaren och redaktionerna ett stort ansvar över att hörsamma sina arbetstagare och tillgodose deras behov av stöd och samtal vid upplevelser av hot. Såväl min uppsats, som tidigare forskning, visar att detta inte alltid fungerar som det borde.

A thermal energy store corrects the misalignment of heating demand in the winter relative to solar thermal energy gathered in the summer. This thesis reviews the viability of a solar charged hot water tank thermal energy store for a school at latitude 56.25N, longitude -120.85W

The implementation of technologies such as aluminum powder metallurgy (P/M) can be used in the automobile industry to have potential economic and environmental advantages. This technology to produce vehicle components can offer the combination of weight savings due to the low density of aluminum and material and machining savings via near net shape processing attributes. In an effort to expand the scope of application for aluminum P/M, considerable research has emphasized the development of new alloys and composites. One such alloy is P/M 2324, an aluminum-copper-magnesium alloy developed to have increased mechanical properties over the standard aluminum P/M alloys of the AC2014 type. The objective of this work was to undertake a comprehensive study on the effects of hot deformation on the emerging alloy P/M 2324 as well as the alloy with a SiC addition. Here, a forgeability study of these alloys and its wrought counterpart AA2024 was completed. To